Hydrolysis of organic phosphorus in soil water suspensions after addition of phosphatase enzymes

Abstract

Additions of enzymes involved in organic phosphorus (P) hydrolysis can be used to characterize the hydrolyzability of molybdate-unreactive P (MUP) in soil water extracts. Our aim was to test the feasibility of enzyme additions to soil water suspensions with respect to (1) suitable enzyme preparations and (2) recovery of molybdate-reactive P (MRP). To this end, we compared the substrate specificity of seven commercially available enzyme preparations (acid and alkaline phosphomonoesterase, phytase, and nuclease preparations) and optimized the assay conditions in microplates. We then measured MRP release after the addition of the enzymes to soil water suspensions and filtrates of two Swiss grassland soils (midland and alpine). In some cases, commercial preparations of the same enzyme differed in their specificity, presumably due to contamination with other enzymes, and also in their efficiency in soil suspensions. Addition of EDTA to the buffer was required to decrease sorption of released P in soil suspensions. Enzymatic release of P was consistently equal or higher in soil suspensions than in soil filtrates. However, also more dissolved MUP was present in soil suspensions than in filtrates, since the buffer interacted with the solid phase. Of the total dissolved MUP in soil suspensions, 94 and 61 % were hydrolyzable in midland and alpine soil, respectively. More specifically, 60 and 17 % of MUP were in nucleic acids, 6 and 39 % in simple monoesters, and 28 and 5 % in inositol hexakisphosphate in midland and alpine soil, respectively. Thus, we show that the characterization of hydrolyzable organic P in soil suspensions with hydrolytic enzyme preparations may be useful to better understand the availability of soil organic P to enzymatic hydrolysis, but that it requires soilspecific adaptation for optimum P recovery.

Characterisation of soil organic phosphorus in NaOH-EDTA extracts: A comparison of 31P NMR spectroscopy and enzyme addition assays

“…Three different enzymes were used: an acid phosphatase from potato (Sigma P1146, 50 units diluted in 15 ml autoclaved H 2 O to reach a catalytic activity of 55.5 nkat ml À1 ) alone or in combination with a nuclease from Penicillium citrinum (Sigma N8630, 0.167 mg diluted in 1 ml autoclaved H 2 O, 550 nkat ml À1 ), as well as a phytase alone from Peniophora lycii (Ronozyme ® NP (Novozyme), 550 nkat ml À1 ). These enzymatic activities were determined to be sufficient by Annaheim et al (2013), who tested different dilutions of the enzymes against model compounds. Since the nuclease hydrolyses only one of the two ester bonds in diesters, nuclease was combined with acid phosphatase to ensure complete hydrolysis of all diesters.…”

The oxygen isotope composition of phosphate released from phytic acid by the activity of wheat and <i>Aspergillus niger</i> phytase

“…Phytases can hydrolyze single phosphomonoester substrates, and some acid phosphatases can partly hydrolyze IP 6 (Gibson and Ullah, 1988;Oh et al, 2004;Annaheim et al, 2013). For this reason, the effect of wheat phytase on adenosine 5 -monophosphate (AMP) and on glycerophosphate (GPO 4 ) used in a previous study (von Sperber et al, 2014) Table 3).…”

Phosphatase activity and culture conditions of the yeast Candida mycoderma sp. and analysis of organic phosphorus hydrolysis ability

“…About 10%-50% is phytate; 1.0%-5.0% is phosphate esters; and 0.2%-5.0% is nucleotide acids. Phosphorus esters are therefore considered to be the major fraction of soil organic phosphorus (Annaheim et al, 2013). Phytin is a phosphorus ester, which can be hydrolyzed by alkaline phosphatase.…”